Among 5% of adults and 15 to 20% of children in western industrial nations asthma is one of the most frequently-occurring diseases, and this tendency is increasing.
Inflammatory conditions of the lower respiratory tracts, such as asthma or bronchiectasis, are accompanied by an increased nitrogen monoxide (NO) concentration of up to 85 ppb in the exhaled air. A reduction in the NO concentration is observed when treated with anti-inflammatory medicines such as corticosteroids. An imminent asthma attack is clearly indicated earlier by the rise in the NO content of the exhaled air than in a pulmonary function test. Nitrogen monoxide is thus a preliminary sign of an asthma attack. Measuring this NO in the exhaled air is thus an ideal method of diagnosis, particularly for deciding treatment and checking the progress of treatment of asthma and other diseases associated with inflammation of the lower respiratory tracts.
A precondition for checking the progress of treatment is, however, a mobile cost-effective measuring instrument for the quantitative detection of nitrogen dioxides regardless of location. A constant telemedical care of chronic diseases would also be of interest.
The accuracy required for the detection of nitrogen oxide in exhaled air in conjunction with the aforementioned diseases is in the area of a few ppb NO. Up to now, this could be achieved only by way of chemo luminescence measurements. The disadvantages are on one hand the size, with a weight of at least 45 kg, and on the other the high cost of such a chemo luminescence measuring apparatus. Up to now, the use of this equipment has been limited to clinics and specialized practices.
At present, peak-flow meters are used to check the progress of, for example, asthma. These are small devices that enable a simple pulmonary function test. In contrast to the complete pulmonary function test, only the highest respiration flow level, the forced expiratory value is measured. This is created at maximum exhalation. The measurement is taken several times a day. The device is relatively inexpensive. However, it measures only the end result of an asthma attack, i.e. the narrowing of the airways, and not a preliminary sign of an attack, such as for example nitrogen monoxide would indicate. Valuable time for preventive treatment is thus lost.
Further evidence of an inflammatory condition of the lower respiratory tracts can also be gained from the bronchial mucus, the sputum. A general sputum examination is macroscopic, microscopic and bacteriological and is comparatively time consuming. Obtaining mucus from children and patients with severe breathing difficulties is either impossible or very difficult.